Because at a device and platform level the N900 and Maemo 5 are basically complete.

Because it's a good open source development practice to share your vision and highlight the main novelties in your roadmap that might affect developers working currently in your platform.

Because it takes a while to productize a new application framework in your platform, leave alone to get ready innovative and attractive hardware, all this with the quality standards we are setting for a Harmattan called to go global and mainstream.

For everything you buy that runs with electricity there is a more advanced version in the works. The strange and suspicious thing would be not to have it.

Announcing Maemo 6 highlights before starting Maemo 5 is being honest to developers and users. I posted more comments in a twin/duplicate thread: http://talk.maemo.org/showthread.php?t=32627

Enjoy Maemo 5!